Numerous devices are presently available for the purpose of tuning musical insturments. Some devices known in the art are mechanical, some are electronic, and other operate on electromechanical principles. A typical electromechanical device known in the art includes a tunable sub-audio oscillator which drives a synchronous electronic motor, which in turn rotates a binary-divided strobe disk. Positioned behind the disk is a glow-discharge tube which flickers in response to the output of a musical instrument. Visual observation of the resulting light pattern provides an indication of the frequency. Numerous difficulties are inherent in this device as well as in other mechanical and electromechanical tuning devices. For example, moving parts are included which are subject to degradation with age and dislocation due to external mechanical shocks. Most devices are heavy and otherwise non-portable. A particular limitation of mechanical and electromechanical devices is the restricted range of frequencies over which operation is effective. Typically, operation is not possible below 25 hertz or above 10K hertz.
A few electronic tuning devices are also known in the art. Typically, such devices are null-reading devices and therefore indicate when a signal frequency is precisely equal to a preset frequency, but do not provide any indication of the amount or direction of tuning error when the signal frequency is not precisely at the preset frequency. The electronic devices heretofore known typically utilize analog electronic circuitry and involve frequency-to-voltage conversions to perform the measurement and provide a display. The accuracy of these analog instruments is therefore limited, even when a highly accurate frequency standard is employed.
It would, therefore, be desirable to have available a digital electronic tuning device whose accuracy was concomitant with that obtainable with digital electronics. Preferably, the device should be portable and easy to read. It should indicate when an incoming signal frequency is equal to a preset frequency, and also provide an indication of the magnitude and direction of the tuning error when the signal frequency is not precisely equal to the reference frequency. When the signal under test comprises a complex waveform, the device should give some indication of the harmonic content of that waveform.